you cannot open any return prior to 2020 using online. only desktop versions may be used if these were timely installed and updated on your computer. if not, they can't be used either. PDF can be uploaded to computer and view using any PDF reader.
other options
1) IRS transcripts for 2017 onward are available either through online transcript or filing form 4506-T. these are free
2016 does not appear to be available
https://www.irs.gov/pub/irs-pdf/f4506t.pdf
2) or for the same years' copies by filing form 4506 fee $30/per year
https://www.irs.gov/pub/irs-pdf/f4506.pdf
3) you can upload each .tax201X tax file and follow onsite instructions. there is a fee - additional for state. This company is not affiliated with Turbotax. Use at your own risk.
https://www.taxprinter.com/
